Method of removing contaminants from petroleum distillates

ABSTRACT

In a method of removing acidic compounds, color, and polynuclear aromatic hydrocarbons, and for removing or converting hydrocarbons containing heteroatoms from petroleum distillates, phase transfer catalyst is employed to facilitate the transfer of inorganic or organic bases to the substrate of the distillate. An inorganic or organic base, a phase transfer catalyst selected from the group including quaternary ammonium salts, polyol ethers and crown ethers, and used oil distillate are mixed and heated. Thereafter, contaminants are removed from the used oil distillate through distillation. A solvent is then mixed with the resulting distillate to extract contaminants therefrom. The solvent is recovered and distilled to separate the contaminants therefrom, and is then reused. The petroleum distillate having the contaminants separated therefrom is also distilled to remove any remaining solvent therefrom, with the recovered solvent being reused.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of Ser. No. 09/465,637 filed Dec. 17,1999, which is a continuation-in-part application of application Ser.No. 09/250,741 filed Feb. 16, 1999, now U.S. Pat. No. 6,007,701 and ofapplication Ser. No. 09/265,903 filed Mar. 10, 1999, currently pending.

TECHNICAL FIELD

This invention relates generally to the removal of contaminants fromused oil, and more particularly to a method of removing acidiccompounds, color, and polynuclear aromatic hydrocarbons, and removing orconverting heteroatoms from petroleum distillates, particularly usedmotor oil distillates.

BACKGROUND AND SUMMARY OF THE INVENTION

It has long been recognized that used motor oils can be recycled byremoving the contaminants which accumulate therein during operation ofthe motor vehicles in which the motor oils are utilized. Recently, theAmerican Society for Testing and Materials (ASTM) has promulgated itsDesignation: D 6074-99 wherein the ASTM Committee D-2 on PetroleumProducts and Lubricants has promulgated standards for re-refined baseoils. Included in Designation: D 6074-99 are numerous attributes of baseoils, including attributes relating to physical properties,compositional properties, chemical properties, and toxicologicalproperties.

Prior to World War II, used, motor oil was re-refined using a processinvolving the addition of sulphuric acid in order to separate thecontaminants from the useful hydrocarbon components of used motor oil.Re-refining processes of the type involving the addition of sulphuricacid to used motor oil are no longer used because they result in thegeneration of large amounts of highly toxic acidic sludge which cannotbe disposed of economically. Additionally, such re-refining techniquesdo not fulfill the requirements of ASTM Designation: D 6074-99.

More recently, used motor oils have been re-refined utilizing a processknown as hydrotreating. In accordance with the hydrotreating process,used motor oils are treated with hydrogen at high temperature andpressure. Hydrotreating is successful in saturating olefins andaromatics in used motor oils and can also be used in removingheteroatoms therefrom. However, the hydrotreating process is expensiveto the point that it cannot be operated profitably.

U.S. Pat. No. 5,814,207 discloses a used motor oil re-refining methodand apparatus wherein up to four evaporators are connected one toanother in a series. It will therefore be understood that the apparatusof the '207 patent is expensive to install and use. More importantly,the used motor oil re-refining method of the '207 patent cannot meet therequirements of ASTM Designation: D 6074-99 because it cannot removeheteroatoms and because it cannot meet the toxicological requirements ofthe designation.

Co-pending U.S. application Ser. No. 09/250,741 filed Feb. 16, 1999, andassigned to the assignee hereof discloses a re-refining process whereinused motor oil is treated with an organic or inorganic base in thepresence of a phase transfer catalyst. The process is successful inremoving acidic compounds and color and in removing or substitutingheteroatoms from used motor oil distillates. Co-pending application Ser.No. 09/265,903 filed Mar. 24, 1999, and also assigned to the assigneehereof discloses a re-refining process wherein used motor oil iscontacted with a highly polar organic solvent, such asN,N-dimethylformamide. The process is successful in removing polynucleararomatic hydrocarbons, sulphur-containing substances,nitrogen-containing substances, and other contaminants from used motoroil and distillates.

The present invention comprises a process for re-refining used motoroils wherein the process of application Ser. No. 09/250,741 and theprocess of application Ser. No. 09/265,903 are operated in series. Theprocess of the invention is unique in that it is the only known processwhich safely and economically fulfills all of the requirements of ASTMDesignation: D 6074-99. dr

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be had by referenceto the following Detailed Description when taken in conjunction with theaccompanying Drawings wherein:

FIG. 1A is the first part of a diagrammatic illustration of a method ofremoving contaminants from petroleum distillates comprising thepreferred embodiment of the invention;

FIG. 1B is a continuation of FIG. 1A;

FIG. 2A is the first part of a diagrammatic illustration of a method ofremoving contaminants from petroleum distillates comprising a variationof the preferred embodiment; and

FIG. 2B is a continuation of FIG. 2A.

DETAILED DESCRIPTION

The process of the present invention removes acidic compounds and colorfrom used motor oil and other petroleum distillates. Additionally, theprocess removes or substitutes hydrocarbons containing heteroatoms,namely chlorine, boron, phosphorous, sulfur and nitrogen from the usedmotor oil. In removing these classes of compounds and to neutralizeorganic acids, the process uses inorganic or organic bases. Further, theprocess is capable of removing polynuclear aromatic hydrocarbons fromused motor oil. The process makes use of a class of catalysts known asphase transfer catalysts, which are employed in the process tofacilitate the transfer of inorganic or organic bases to the substratein the used oil.

Examples of phase transfer catalysts that may be utilized in the processinclude: quaternary ammonium salts, polyol ethers, glycols and crownethers. Through either the base catalysts or the neutralizationreactions, undesirable components of the distillate oil are most oftenconverted to forms that are easily removed from the used oil throughdistillation. Components that are not removed from the distillate aretransposed to forms that may remain in the distillate with no adverseeffect on the oil quality.

The invention is capable of operating in either a batch mode or acontinuous flow mode. When operated in the batch mode, used oil iscontacted with a phase transfer catalyst and a base. Heat is applied andthe mixture is vigorously stirred. After the appropriate reaction time,the base and catalyst are washed out of the used oil with water, afterwhich the remaining oil is distilled. For best results in the batchprocess, the initial used oil should be wide cut oil prepurified by widecut distillation.

When the process is operated in the continuous flow mode, the oil, base,and catalyst are heated and mixed in appropriate order, passing throughheat exchangers, in-line mixers, and tanks as required to effectivelytreat the oil. The mixture is then passed directly to the distillationapparatus, where additional mixing occurs and the catalyst and resultingoil are recovered as separate streams. The catalyst is recovered in ahighly purified form and may be reused.

Although other phase transfer catalysts can be used in the process, theuse of ethylene glycol is preferred because, when ethylene glycol isused, the source of the catalyst can be used with glycol-based enginecoolants. Thus, the catalyst can be acquired in raw form with little, ifany, expenditure.

Following removal of the catalyst and distillation of the lubricatingoil cuts, the distilled oil is directed to a liquid/liquid extractionapparatus. The distillate and a solvent, preferably a higher polarorganic solvent such as N,N-dimethylformamide, are counter-flowedthrough the extraction apparatus, whereby the solvent removescontaminants from the distillate. Typical types of extraction devicesinclude mixer/settler combinations, non-agitated columns, and agitatedcolumns. The following discussion assumes the use of a Karr column,which is an agitated column design.

A process for removing contaminants from used motor oil 10 comprising acontinuous flow process is shown in FIGS. 1A and 1B. In the process 10,the used oil from a source 12 is passed through a used oil feed pump 14to a heater 16. At the same time, an aqueous solution of a base, e.g., a50% aqueous solution of sodium or potassium hydroxide, is directed froma source 18 through a base feed pump 20 and into the used oil after itpasses through and is heated to 70 to 125° C. by the heater 16. Theamount of base added to the used oil is such that the concentration ofbase in the oil, on a dry weight basis, is between 0.5 and 5 weightpercent. The used oil and base pass through an in-line mixer 22 and aheater 24, heating the mixture to 110 to 160° C. The used oil mixture isthen passed into a water flash drum 26 where water and a small amount ofnaphtha are removed through flash outlet 28. The water flash drum isbest operated at low positive pressure, e.g., 0.8 to 1.1 barg., thusallowing a higher feed temperature to promote the reactions. However, inprinciple the flash drum could operate under vacuum. The resultantdehydrated used oil mixture is then removed from the water flash drum 26through a flash oil outlet 30.

A phase transfer catalyst from a source 32 is passed through a catalystfeed pump 34 and into the dehydrated used oil mixture. The amount ofphase transfer catalyst that is added to the used oil is such that theconcentration of catalyst in the resulting mixture ranges from 1 to 10weight percent of the used oil. The used oil feed pump 14, the base feedpump 20, and the catalyst feed pump 34 are each engaged at flow ratesthat provide the desired amounts of each material. The used oil mixtureis passed through an in-line mixer 36 and a heater 38, where it isheated to between about 275 and 350° C., blended with the recycledbottoms stream from recycle pump 46, passed through in-line mixer 47,heated in heater 48, and directed into a stage I evaporator 40. Heatingthe mixture beyond 350° C. is not recommended as temperatures above 350°C. can result in excessive cracking of the used oil molecules. The stageI evaporator is typically operated under vacuum, with pressures rangingfrom about 150 to 300 millimeters of mercury. The catalyst and lighthydrocarbons are removed through flash catalyst outlet 42 and the oil isremoved through oil outlet 44. Part of the oil passes through a recyclepump 46 and back into the dehydrated used oil mixture after the in-linemixer 36, but before the heater 48.

The remainder of the oil passes through a stage II feed pump 49 and aheater 50, where it is heated to from about 300 to 350° C., and into astage II evaporator 52. The stage II evaporator operates under vacuumwith pressures ranging from 0.5 to 5 millimeters of mercury. The stageII evaporator may be operated at lower temperatures, but this willresult in a lower yield of the heavier base oil product. The stage IIevaporator separates the oil into three fractions, the viscosities ofwhich depend upon the used oil feed. The table below lists products froma typical used oil feed:

Viscosity @ Fraction Color Chlorine 40° C. light base oil <0.5 <5 ppm100 SUS medium base oil <1.0 <5 ppm 150 SUS heavy base oil <1.5 <5 ppm300 SUS still bottoms n/a n/a n/a

The light base oil is recovered through outlet 54, the medium base oilthrough outlet 56, the heavy base oil through outlet 58, and the stillbottoms through outlet 60.

The still bottoms resulting from the simultaneous combination of thecatalyzed base treatment with distillation yields important propertieswhen combined with asphalt. In general, the still bottoms comprise ahigh value asphalt modifier, capable of extending the useful temperaturerange of most straight run asphalts. Specifically, the still bottomsimpart favorable low temperature characteristics to asphalt, whilemaintaining the high temperature properties of the asphalt.

Part of the still bottoms are directed through a pump 62 and arerecirculated through a line 53 and the heater 50 into the stage IIevaporator. The light base oil, medium base oil, and heavy base oil eachflow to a dedicated holding tank. Each of the base oils is fed to theextraction section in sequence in blocked operation, i.e., a tank oflight base oils processed, then a tank of medium base oil, then a tankof heavy base oil, then the cycle repeats.

Referring to FIG. 1B, the oil is directed through a tank 68 and a pump70 and a heat exchanger 72 to the bottom of an extraction apparatus 74,such as a Karr column. Simultaneously a solvent is directed from asource 76 through a pump 78 and through a heat exchanger 80 whichincreases the temperature of the solvent to the top of the Karr column74. The solvent which is utilized in the practice of the inventionpreferably comprises a highly polar organic solvent, such asN,N-dimethylformamide (DMF). Other solvents in the class acetonitrilemay also be used in the practice of the invention. The polarity of thesolvent may be adjusted by the addition of water and/or other materialsdepending upon the requirements of particular applications of theinvention.

The Karr column 74 comprises a tank 82 having a rod 84 verticallydisposed therein. A plurality of shelves 86 are secured to the rod 84for vertical reciprocation thereby. The rod 84 extends to an actuator 88which functions to reciprocate the rod 84 and the shelves 86 verticallyat a predetermined rate.

Each of the shelves 86 has a plurality of holes formed therethrough.Because the solvent from the source 76 is relatively more dense, ittends to move downwardly in the tank 82 relative to the upwardly movingpetroleum. Conversely, because the petroleum distillate is relativelyless dense, it tends to move upwardly in the tank 82 relative to thesolvent. The vertical reciprocation of the shelves 86 and the fact thatthe shelves 86 have holes therethrough substantially increases thesurface area between upwardly moving petroleum and the downwardly movingsolvent. By this means the solvent functions to extract contaminantswhich are present in the petroleum distillate therefrom, and to carrythe extracted contaminants upwardly out of the tank 82.

The solvent having the contaminants from the petroleum distillatedissolved therein is recovered from the tank 82 through an outlet 89 andis directed to a surge tank 90. From the surge tank 90 thesolvent/contaminant solution is directed through a pump 92 and through aheat exchanger 94 which increases the temperature of the solution to afalling film evaporator 96.

The falling film evaporator 96 is heated by a heating medium, e.g.,steam or thermal oil, which is received through an inlet 98 andrecovered through an outlet 100. The falling film evaporator 96functions to evaporate the solvent, thereby separating the solvent fromthe contaminants dissolved therein. The contaminants are recovered fromthe falling film evaporator 96 through an outlet 102. The contaminantsflow through a surge tank 104 to a pump 106 which directs thecontaminants to suitable utilization apparatus. For example, thecontaminants may be directed to an asphalt storage tank, or blended intoplant fuel and burned.

The solvent is recovered from the falling film evaporator 96 through anoutlet 110 and is directed to heat exchangers 112 and 118 which removeheat from the solvent. Solvent from exchanger 118 is directed through anoutlet 114 to a surge tank 116. Solvent which remains in the vapor stageis directed to a vent 122. Solvent from the surge tank 116 is directedthrough an outlet 124 to a pump 126 which returns the solvent to thesource 76.

Petroleum distillate having the contaminants removed therefrom isrecovered from the tank 82 through an outlet 130 and is directed to asurge tank 132. From the surge tank 132 the petroleum distillate isdirected through a pump 134 and through a heat exchanger 136 which addsheat to the petroleum distillate to a falling film evaporator 140. Thefalling film evaporator 140 is actuated by steam which is receivedthrough an inlet 142 and recovered through an outlet 144.

The falling film evaporator 140 functions to remove any remainingsolvent from the petroleum distillate. The solvent is recovered from thefalling film evaporator 140 through an outlet 146 and is directed toheat exchangers 148 and 152 which remove heat from the solvent. Solventrecovered from the heat exchanger 152 is directed to a surge tank 150.Any solvent remaining in the vapor phase is directed to a vent 154.Liquid solvent from the surge tank 150 is directed to a pump 156 whichreturns the solvent to the source 76 through the tank 116 and the pump126.

Petroleum distillate having substantially all polynuclear aromatichydrocarbons, sulphur and nitrogen-containing substances and othercontaminants removed therefrom is recovered from the falling filmevaporator 140 through an outlet 160. The petroleum distillate passesthrough a surge tank 162 and from the surge tank 162 to a pump 164 whichdirects the petroleum distillate to storage facilities and/or furtherprocessing apparatus.

Referring particularly to FIG. 1A, the water, any glycol contained inthe used oil feed, and light hydrocarbons from the flashdrum 26 aredirected through the outlet 28 to a condenser 170, and from thecondenser 170 to a liquid/liquid separator 172. The catalyst and lighthydrocarbons from the stage I evaporator are directed through the flashcatalyst outlet 42 and through a condenser 174 to a liquid/liquidseparator 176. The less dense liquid from the separator 176 is directedthrough a pump 178 and is recovered at an outlet 180. The heavier liquidfrom the separator 176 is directed through pump 182 to the separator172.

Vapors and gases from the separator 172 are vented at an outlet 184.Less dense liquid from the separator 172 is directed through a pump 186and are recovered at the outlet 180. More dense liquid from theseparator 172 is directed through a pump 188 to a heater 190 where theheavy liquid recovers heat from the dry catalyst leaving the bottom ofthe distillation tower 194. Cooled dry catalyst from the heater 190comprises dry catalyst which is returned to the source 32 through a line192. The heated heavy liquid from the heater 190 is directed through adistillation tower 194.

The distillation tower 194 separates the feed into low boiling and highboiling cuts. The low boiling cut is directed through an outlet 196through a condenser 198, and from the condenser 198 to a receiver 200.Gases are vented from the receiver 200 through outlet 202. Liquid fromthe receiver 200 is directed to a pump 204. Part of the output of thepump 204 is returned to the distillation tower 194. The remainder of theoutput of the pump 204 is directed to a coalescer 206. Light liquid fromthe coalescer 206 is directed to the separator 172 through a line 208.Waste water is recovered from the coalescer 206 through an outlet 210.

The heavy cut from the distillation tower 194 is directed to a pump 212.Part of the output of the pump 212 is directed to the heater 190. Theremainder of the output from the pump 212 is directed through a heater214 and is returned to the distillation tower 194.

FIGS. 2A and 2B illustrate a system 220 for removing polynucleararomatic hydrocarbons and other contaminants from petroleum distillatecomprising a second embodiment of the invention. The system 220 includesnumerous component parts which are substantially identical inconstruction and function to the component parts of the system 10illustrated in FIGS. 1A and 1B and described hereinabove in connectiontherewith. Such identical component parts are designated in FIGS. 2A and2B with the same reference numerals utilized above in the description ofthe system 10, but are differentiated thereof by means of a prime (′)designation.

The system 220 of FIGS. 2A and 2B differ from the system 10 of FIG. 1 inthat the system 220 is utilized in those instances in which the solventis lighter, i.e., less dense, than the petroleum distillate. In suchcases the solvent is directed to the bottom of the tank 82′ and isrecovered from the top thereof after extracting the polynuclear aromatichydrocarbons from the petroleum distillate. Conversely, the petroleumdistillate is directed to the top of the tank 82′ and is recovered fromthe bottom thereof following removal of the polynuclear aromatichydrocarbons and other contaminants from the petroleum distillate by theaction of the solvent. Otherwise, the operation of the system 300 ofFIGS. 2A and 2B is virtually identical to the operation of the system 10of FIGS. 1A and 1B.

The present invention is highly successful in improving the quality ofused oil distillates. Thus, in the practice of the invention, theconcentration of polynuclear aromatic hydrocarbons in used oildistillates is reduced from about 200 ppm to about 1 ppm or to evenlower concentrations depending upon the requirements of particularapplications of the invention. The use of the method of the invention isalso successful in reducing the color of used oil distillates to a levelcomparable with that of used oil distillates that have beenhydrotreated.

Although preferred embodiments of the invention have been illustrated inthe accompanying Drawings and described in the foregoing DetailedDescription, it will be understood that the invention is not limited tothe embodiments disclosed, but is capable of numerous rearrangements,modifications, and substitutions of parts and elements without departingfrom the spirit of the invention.

We claim:
 1. A method of purifying used oil comprising the steps of:providing a predetermined quantity of used oil; contacting the used oilwith a base in a predetermined quantity such that the concentration ofbase in the oil, on a dry weight basis, is between about 0.05 and about5 weight percent; contacting the used oil with a phase transfer catalystin a predetermined quantity such that this concentration of catalyst inthe base-oil mixture is between about 1.0 and about 10 weight percent ofthe oil; thoroughly mixing the composition comprising used oil, base,and phase transfer catalyst; heating the composition to a temperature ofbetween about 275° C. and about 350° C.; distilling the resultantmixture; mixing the resulting distillate with a solvent therebydissolving the contaminants from the petroleum distillate into thesolvent; separating the solvent having the contaminants dissolvedtherein from the petroleum distillate; subsequently separating thecontaminants from the solvent and recovering the solvent; and recoveringany remaining solvent from the petroleum distillate.
 2. The methodaccording to claim 1 wherein the phase transfer catalyst comprisesethylene glycol.
 3. The method according to claim 1 wherein the solventcomprises N,N-dimethylformide.
 4. The method according to claim 1wherein the phase transfer catalyst comprises ethylene glycol and thesolvent comprises N,N-dimethylformidine, and the base is a hydroxide. 5.A process for purifying used oil comprising the steps of: blending apredetermined quantity of used oil and a predetermined quantity of abase; blending the composition comprising used oil and base with apredetermined quantity of phase transfer catalyst; mixing thecomposition comprising used oil, base, and phase transfer catalyst for apredetermined period of time; heating the composition to a temperatureof between about 275° C. and about 350° C.; distilling the resultantmixture; mixing the resulting distillate with a solvent therebydissolving the contaminants from the petroleum distillate into thesolvent; separating the solvent having the contaminants dissolvedtherein from the petroleum distillate; subsequently separating thecontaminants from the solvent and recovering the solvent; and recoveringany remaining solvent from the petroleum distillate.
 6. The processaccording to claim 5 comprising the additional step of: heating saidbase to a predetermined temperature before blending said base and saidused oil.
 7. The process according to claim 6 further characterized by:heating a predetermined quantity of a base selected from the groupconsisting of 50% aqueous solution of sodium hydroxide and 50% aqueoussolution of potassium hydroxide to a temperature of between about 70° C.to about 125° C.
 8. The process according to claim 7 wherein thepredetermined quantity of base comprises a concentration of said base insaid oil, on a dry weight basis, of between about 0.5 percent and about5 percent.
 9. The process according to claim 8 comprising the additionalstep of: heating the composition comprising used oil and base to atemperature of between about 110° C. and about 160° C.
 10. The processaccording to claim 5 wherein the base is selected from the groupincluding sodium hydroxide and potassium hydroxide.
 11. The processaccording to claim 5 wherein the phase transfer catalyst is selectedfrom the group consisting of quaternary ammonium salts, polyol ethers,glycols and crown ethers.
 12. A process for purifying used oilcomprising the steps of: heating a predetermined quantity of a base to apredetermined temperature; mixing a predetermined quantity of used oiland said heated base; dehydrating the composition comprising used oiland base; contacting the composition comprising used oil and base with apredetermined quantity of phase transfer catalyst; thoroughly mixing thecomposition comprising used oil, base, and phase transfer catalyst;heating the composition to a temperature of between about 275° C. andabout 350° C.; distilling the resultant mixture; mixing the resultingdistillate with a solvent thereby dissolving the contaminants from thepetroleum distillate into the solvent; separating the solvent having thecontaminants dissolved therein from the petroleum distillate;subsequently separating the contaminants from the solvent and recoveringthe solvent; and recovering any remaining solvent from the petroleumdistillate.
 13. The process according to claim 12 wherein the phasetransfer catalyst is selected from the group consisting of quaternaryammonium salts, polyol ethers, glycols and crown ethers.
 14. The processaccording to claim 12 wherein the base is selected from the groupincluding sodium hydroxide and potassium hydroxide.